Re: >20kHz content found in vinyl?

2017-08-21 00:46:03

Looking at rips fo DVD-A, SACDs, BluRay relases of old analog recordings, where the tapes were transferred to digital at >16/44, I quite often see a straight line (or rarely, two) in ultrasonic regions of spectral views, representing inaudible hum/buzz from video monitors in the recording/mixing/mastering studio. That's 'original' but it's noise rather than signal...original noise, I guess we can call it.

I've found this line present in a 24/96 copy I've made of the 2009 release of Nirvana's Nevermind (it shows all across the record, both sides). The record was mastered by Bernie Grundman from the original analog master tapes ... do you think this is one of those cases or maybe the "line" may also be present in the master tapes?

Re: >20kHz content found in vinyl?

I've found this line present in a 24/96 copy I've made of the 2009 release of Nirvana's Nevermind (it shows all across the record, both sides). The record was mastered by Bernie Grundman from the original analog master tapes ... do you think this is one of those cases or maybe the "line" may also be present in the master tapes?

When you say "across the record, both sides", I take it that you're referring to a vinyl LP that you've transferred?In which case, have you considered the possibility that it is not on the LP but was introduced by something during the digital transfer?

Re: >20kHz content found in vinyl?

Looking at rips fo DVD-A, SACDs, BluRay relases of old analog recordings, where the tapes were transferred to digital at >16/44, I quite often see a straight line (or rarely, two) in ultrasonic regions of spectral views, representing inaudible hum/buzz from video monitors in the recording/mixing/mastering studio. That's 'original' but it's noise rather than signal...original noise, I guess we can call it.

I've found this line present in a 24/96 copy I've made of the 2009 release of Nirvana's Nevermind (it shows all across the record, both sides). The record was mastered by Bernie Grundman from the original analog master tapes ... do you think this is one of those cases or maybe the "line" may also be present in the master tapes?

Re: Re: >20kHz content found in vinyl?

I'd say this is good evidence of high frequency content in vinyl. That's the 30Khz carier (i forget the real name, but it's added to tape recording in order to make the requency response more linear). It's certainly not distortion.

Re: Re: >20kHz content found in vinyl?

I'd say this is good evidence of high frequency content in vinyl. That's the 30Khz carier (i forget the real name, but it's added to tape recording in order to make the requency response more linear). It's certainly not distortion.

The solid line could be bias but 28kHz is kind of low for that, and we need more info about the recording to be sure. Everything around it, the fuzzy stuff, is probably distortion. Regardless, none of it is supposed to be there, it wasn't in the original soundfield, and so any of it, bias or not, is a type of distortion.

Re: >20kHz content found in vinyl?

Seems like this was split off the original thread ( https://hydrogenaud.io/index.php/topic,113365.0.html ). Possibly over discussing > 20 kHz found in (digitized versions mastered from) analogue master tapes, maybe that was considered off-topic. De-railing this thread back to vinyl is maybe not necessary, as long as we have the original thread (and maybe even less necessary if, people read before posting).

Re: Re: >20kHz content found in vinyl?

I'd say this is good evidence of high frequency content in vinyl. That's the 30Khz carier (i forget the real name, but it's added to tape recording in order to make the requency response more linear). It's certainly not distortion.

The solid line could be bias but 28kHz is kind of low for that, and we need more info about the recording to be sure. Everything around it, the fuzzy stuff, is probably distortion. Regardless, none of it is supposed to be there, it wasn't in the original soundfield, and so any of it, bias or not, is a type of distortion.

Bias, that’s the word I was looking for! Also I don’t understand why we think that vinyl can’t have frequencies above 20KHz. It’s a plastic disc, rubbing a needle that moves a magnet. Theres not hard limit really. You can argue that it’s mostly distortion but there’s certainly no reason not to encode high frequencies in vinyl.

I realise now I can test this. I have that record from Jack White, and there is HD digital recordings of it too. Comparison would be interesting

Re: >20kHz content found in vinyl?

Bias, that’s the word I was looking for! Also I don’t understand why we think that vinyl can’t have frequencies above 20KHz. It’s a plastic disc, rubbing a needle that moves a magnet. Theres not hard limit really.

Not a hard limit, as in an anti-aliasing filter is a hard limit, but there is a maximum stylus velocity curve dictated by the dimensions of the groove and length of the cutter stylus. Causing excessive stylus velocity rams the back facet of the stylus into the groove wall it just cut. That is a "hard limit", but it's a function of both frequency and modulation. It happens at lower levels of higher frequencies, and higher levels of lower frequencies, but it happens, and must be accounted for. The RIAA curve actually makes it a bit worse of a problem at very high frequencies, hence the application of high frequency limiting in disc cutting.

I don't think there's anyone arguing that vinyl cannot record higher than 20kHz information, it's just a question of how much and how well. Remember that CD4 records employed a pair of 30kHz carriers with a type of modified FM on them, but the result still contained sidebands. The carriers were very low in level, though, and required a special stylus for proper recovery. So there's no absolutely yes or no to the above 20kHz question, it's more of an "it depends" answer.

I realise now I can test this. I have that record from Jack White, and there is HD digital recordings of it too. Comparison would be interesting

Probably won't show much difference, though, because analog tape contains high levels of high frequency distortion of several types, and you said this was from an analog master. The content, other than the bias signal, could still be distortion products that are generated by tape's nonlinearities. Remember that distortion in analog tape is a function of fluxivity (level) and that changes with an EQ curve making high frequencies distort and saturate before lower ones.

Re: >20kHz content found in vinyl?

So my post was binned due to the ambiguous TOS2 so let me express my opinion in an unambiguous way. As stated at the earlier part (before the split) of this thread, I think the only reliable way to test this thing is to find some vinyl cutting service providers and cut some known test signals on vinyls and re-digitize them.

I don't trust any spectrograms and even videos showing animated FFT analysis for vinyl rips of unverifiable sources.

The sweep on that LP stops at 20 kHz, why? Could it be because > 20 kHz content is nothing to care about?[edit: note]

(Wouldn't it be a better business idea to cut a sweep up to, say, 30 kHz? If the self-proclaimed golden ears cannot hear it, they surely need to upgrade their gear into something which can reproduce it. And then if the placebo still cannot convince them that they hear, then apparently their previous stylus wore down the old test LP - so buy another! And argh, you have to to re-purchase all the LPs you have actually played with the old stylus?)

Re: >20kHz content found in vinyl?

It doesn't seem normal to me if for example a 96kHz sweep suddenly drops at somewhere around 20kHz after being cut on a vinyl unless the lathe has some circuitry to do that. I am more interested to know if recording such a high frequency signal on a vinyl will significantly increase the distortion at the lower end (below 20kHz) of the spectrum. The twin tone IMD swept from RMAA for example makes a great test signal for this purpose.

Normal music has a lot of content below 20kHz, it is impossible to differentiate real content from distortion by using them as test signal.

Re: >20kHz content found in vinyl?

It doesn't seem normal to me if for example a 96kHz sweep suddenly drops at somewhere around 20kHz after being cut on a vinyl unless the lathe has some circuitry to do that. I am more interested to know if recording such a high frequency signal on a vinyl will significantly increase the distortion at the lower end (below 20kHz) of the spectrum. The twin tone IMD swept from RMAA for example makes a great test signal for this purpose.

Normal music has a lot of content below 20kHz, it is impossible to differentiate real content from distortion by using them as test signal.

The attachment is an interesting relevant example.

The lower trace is of a quiet passage on the LP.

Due to the low recorded level there is evidence of negligible amounts of nonlinear distortion. Interesting enough, there is clear evidence of a brick wall filter @ 22-24 Khz cutting a hole in the noise floor. There is also a 24 KHz "birdie" spiking up out of the noise floor. I believe this is due to the use of an Ampex AD-1 digital delay line or equivalent in the groove pitch automation system for the cutting lathe which was not uncommon when this disk was first mastered.

The upper trace shows same LP and playback system playing a loud passage. Since we know that there was a brick wall filter @ 22-24 KHz, everything above that must be due to nonlinear distortion in the record and playback system downstream of the AD-1.

Re: Re: >20kHz content found in vinyl?

Also I don’t understand why we think that vinyl can’t have frequencies above 20KHz.

Nobody thinks that. Why do you think someone does?

Because it is an article of faith among vinyl advocates that all criticism of vinyl is unreasonable and fomented by people who judge it unfairly?

Quote

That a vinyl record can be pressed with frequencies >20khz has been known for many decades. However, there is no evidence that the human ear can hear them or that they are musically meaningful.

Case in point would be the post I just made about brick wall filtering that is "baked into" many legacy LPs. For this post to make sense I had to confirm that it is possible to record signals at low levels at frequencies > 24 KHz. The fact that the stop band around 24 kHz shows up clearly and accurately is a testimonial to vinyl's ability to handle low-level signals > 24 kHz.

However, the example shows that the relatively high nonlinear distortion (THD, IM) that is inherent in the LP format adds substantial amounts (> 3%) of spurious responses. The nonlinear distortion comes from several sourced, but the problem of tracing the groove accurately with a finite sized stylus dominated. For example:

Tracing distortions are quite separate from tracking distortions. The origin of all tracing distortion is that a groove cut by a flat-faced chisel is being read by a rounded (conical or elliptical) stylus. Tracing distortion is responsible for the majority of distortion (and not just harmonic distortion) when reproducing gramophone records. There are three components to tracing distortions: pinch-effect; vertical tracing distortion; and tracing-loss.

Pinch effect

Constrained as it is to follow a path along the disc radius, the cutter chisel cuts a groove which is only the width of the cutter at the peaks of the wave and which shrinks to a minimum as the wave passes through the zero position. This has the effect of squeezing the stylus up and down in the groove even when the modulation is entirely lateral. This phenomenon is termed, appropriately enough, pinch effect.

This effect of pinching the stylus in the narrowing groove may be seen to be at a frequency double that of the lateral modulation; because the stylus rises and falls twice over in one cycle of the modulation wave (see the illustration left).The pinch-effect upon the stylus is greater as the wavelength of the modulation falls. Besides being frequency dependent, wavelength is also a function of the angular velocity of the recording chisel in the groove. In a conventional gramophone record, this velocity falls as the cutter (or stylus) moves towards the centre of the record because the record turns at a constant number of revolutions per minute, but the radius of the groove falls throughout the playing of one side of the disc.

Additionally, the degree of the pinch-effect depends upon the radius of the stylus. Special stylus shapes have been developed to reduce the pinch-effect. Elliptical styli are shaped so that the major axis of the ellipse has the dimensions of a conical stylus and is perpendicular to the groove. This ensures the stylus rides in the groove at the same level as a conical stylus and doesn't wallow about in the bottom of the groove where no information resides. However, the minor axis of the ellipse is arranged to be considerably smaller than the major axis and this is parallel with the groove. By these means, the stylus is less squeezed as the groove narrows in the direction of the stylus travel."